I agree! Atheism is not a belief system, it is a lack of belief in gods. Any gods. Atheists may have other beliefs, which have nothing to do with the existence, or not, of gods. Just as Christians, or Jews, or Muslims can have other beliefs aside from their gods. The difference is that atheists do NOT try to force their beliefs on others. We DO try to prevent theists from forcing their beliefs upon us.
This is a big problem with theists. Especially those who, for example, declare the Bible to be inerrant. Some of these people will argue and complain that evolution is false, they will deny any evidence which supports evolution, they will twist evidence to try to make it fit their preconceived belief systems, then complain when we don't accept their assertions about their god. If they refuse to accept real, documented, verifiable, falsifiable evidence about something as real as evolution, why should we be expected to accept their imagined, poorly documented, unverifiable, unfalsifiable assertions about mystical beings?It is not the job of the atheist to prove that God does not exist. It is the job of the believer to prove that God does.